1. Field of the Invention
Polyphenylene ethers (PPE) are high-performance engineering thermoplastics with high melt viscosities and high softening points. They are used especially where stability at high temperatures is needed (see U.S. Pat. Nos. 3,306,874, 3,306,875, 3,257,357, and 3,257,358). Shaped parts made of pure polyphenylene ethers are brittle because of their poor impact strength, and their solvent resistance is unsatisfactory. Therefore, mixtures of polyphenylene ethers with other thermoplastics are generally used.
Blends of polyphenylene ethers with polyamides show good solvent resistance and good flowability (DE-OS 16 94 290 and JP-OS 78/47,390). Usually, however, brittle products are obtained since the two components are incompatible.
It has, therefore, been suggested that the compatibility of the two polymers be increased by adding a sufficient quantity of a flow agent, for example an organic phosphate (EP-OS 0 129 825) or a diamide (EP-OS 0 115 218). However, the improved compatibility is accompanied by substantially reduced dimensional heat stability. Molding compositions to which have been added copolymers of styrene and unsaturated acid derivatives have the same drawback (EP-OS 0 046 040).
The object of European Pat. No. 0 024 120 is resin compositions that consist of a polyphenylene ether, a polyamide, a third component, and optionally high molecular weight rubbers. A liquid diene polymer, an epoxide, or a compound with a double or triple bond and a functional group (for example, an acid, anhydride, ester, amino, or alcohol group) is used as the third component. However, the toughness of the resin compositions obtained is inadequate for many applications.
Better compatibility of the two phases is achieved by functionalizing the polyphenylene ether, for example with maleic anhydride in the presence of sources of free radicals (JP-OS 84/066,452). Of course, this advantage is obtained at the expense of partial crosslinking of the PPE phase. In WO 87/00 540, the functionalizing of polyphenylene ethers with maleic anhydride without sources of free radicals is sufficiently successful only in the presence of special triblock copolymers, while in U.S. Pat. No. 4,654,405, the reaction of powdered polyphenylene ether with maleic anhydride, likewise in the absence of radical sources, and further blending with polyamides, is described. However, the degree of functionalizing in this case is still inadequate.
The functionalizing of polyphenylene ethers by reaction of the polymers with hydroxypolycarboxylic acids or their derivatives in the melt is described in EP-OS 0 185 054. After blending with polyamides, molding compositions are obtained whose crack growth and notched impact test results reveal unsatisfactory bonding at the phase interfaces.
The object of EP-OS 0 195 815 is the functionalizing of polyphenylene ethers with trimellitic anhydride acid chloride in solution. Blends with polyamides do tend to be better than in the prior case, but because of the described functionalizing, either hydrogen chloride escapes, or considerable amounts of ammonium chlorides are formed when a tertiary amine is added, and corrosion problems therefore arise. The economically interesting direct isolation of the polyphenylene ether by removing the solvent cannot be used in this case.
A combination of polyphenylene ethers and polyamides is described in EP-OS 0 211 201, that is made by capping the terminal OH groups of the polyphenylene ether, followed by polymerization of a lactam. The capping agent in this case acts as a promoter for the lactam polymerization. Examples of suitable promoters are maleic anhydride, cyanuric chloride, N,N'-carbonyldiimidazole, and phenyl chloroformate. However, these compositions are unsatisfactory in practice. The functional groups of the promoters are chemically unstable, and the limitation to polyamides that are obtained by polymerization of lactams is limiting.
DE-OS 36 00 366 describes thermoplastic molding compositions that contain as essential components a polyphenylene ether, a comb polymer with a hydrocarbon as the main chain and polyphenylene ethers as sidechains, a functionalized polyethylene, and a polyamide. The compositions are therefore true complex mixtures in which each of the four components is necessary to provide both good compatibility and high impact strength and dimensional heat resistance. It would be desirable if these objectives could also be reached in a simpler way.
DE-OS 36 15 393 and OS 36 21 805 describe molding compositions that contain a remelted preformed composition in addition to a polyamide. The preformed composition consists of a polyphenylene ether, a polyoctenylene, and at least one acid component such as maleic anhydride. In both cases, it is necessary to melt the polyphenylene ether with a chemically aggressive acid component and to add an impact strength promoter to reach a qualitatively satisfactory level of notched impact strength. A similar process is described in EP-OS 0 232 363.
The process described in JP-OS 84/86,653 provides for grafting 100 parts of polyphenylene ether by a radical process with 10 to 300 parts of a mixture of 50 to 99% styrene and 50 t 1% unsaturated carboxylic acids or anhydrides and blending the product with polyamides. The molded parts formed have good mechanical properties, but the dimensional heat stability is impaired by the considerable proportion of styrene. When it is attempted to compensate for this drawback by increasing the proportion of anhydride, molding compositions with severely impaired properties are obtained, for example inadequate impact strength and notched impact strength.
European Pat. No. 0 147 874 tries not to detract from the dimensional heat resistance by adding small amounts (0.1-1.9 wt.%) of a styrene-maleic anhydride copolymer (41 to 50 mole-% maleic anhydride) to a mixture of polyphenylene ethers and polyamides. However, the examples show that no improvement of the completely inadequate mechanical characteristics is obtained by this addition, probably because of the inadequate interaction with the polyphenylene ether.
The molding compositions known from the state of the art, therefore, can either be produced only at high cost, or the molded parts produced from them have unsatisfactory properties. It is the purpose of this invention to avoid these drawbacks.